Many documents are known describing processes for the catalytic conversion of (gaseous) hydrocarbonaceous feedstocks, especially methane, natural gas and/or associated gas, into liquid products, especially methanol and liquid hydrocarbons, particularly paraffinic hydrocarbons. In this respect often reference is made to remote locations and/or off-shore locations, where no direct use of the gas, e.g. through a pipeline or in the form of liquefied natural gas, is not always practical. This holds even more in the case of relatively small gas production rates and/or fields. Reinjection of gas will add to the costs of oil production, and may, in the case of associated gas, result in undesired effects on the crude oil production. Burning of associated gas has become an undesired option in view of depletion of hydrocarbon sources and air pollution.
The Fischer Tropsch process can be used for the conversion of hydrocarbonaceous feed stocks into liquid and/or solid hydrocarbons. Generally the feed stock (e.g. natural gas, associates gas and/or coal-bed methane, coal) is converted in a first step into a mixture of hydrogen and carbon monoxide (this mixture is often referred to as synthesis gas or syngas). The synthesis gas is then fed into a reactor where it is converted in one or more steps over a suitable catalyst at elevated temperature and pressure into paraffinic compounds ranging from methane to high molecular weight modules comprising up to 200 carbon atoms, or, under particular circumstances, even more.
Catalysts used in the Fischer-Tropsch synthesis often comprise a carrier based support material and one or more metals from Group VIII of the Periodic Table, especially from the iron group, optionally in combination with one or more metal oxides and/or metals as promoters selected from zirconium, titanium, chromium, vanadium and manganese, especially manganese. Such catalysts are known in the art and have been described for example, in the specifications of WO 9700231A and U.S. Pat. No. 4,595,703.
Catalysts can be prepared by obtaining a metal hydroxide, carefully oxidising it to the metal oxide and then placing it in the appropriate reactor where it is reduced to the metal in situ.
One catalyst or catalyst precursor for Fischer-Tropsch reactions is a shaped catalyst or catalyst precursor comprising cobalt and titania. To prepare the catalyst, cobalt hydroxide (CO(OH)2) can be used as a starting material. This material is usually mixed with one or more co-catalysts, promoters, titania, etc, shaped, for example formed into mm sized particles by means of extrusion, and then calcined. During the calcination Co3O4 is formed. After calcination the catalyst or catalyst precursor is placed in a Fischer-Tropsch reactor. In the reactor the cobalt compound(s) is (are) reduced to cobalt.
Sometimes a mixture of a catalytically active metal or metal compound and a carrier material, a shaped mixture and a calcined (shaped) mixture are referred to as catalyst precursor or catalyst. Sometimes a shaped mixture and a calcined shaped mixture are referred to as catalyst preformer. In this specification a mixture comprising catalytically active metal or metal compound and carrier material will be referred to as “catalyst or catalyst precursor”, irrespective of any shaping or forming, for example spray-drying and especially extrudation, calcination, reduction, and/or any other process step it may have been subjected to.
Hitherto, there has been no consideration of the process for combining and calcining the catalytically active metal and promoter(s) etc. Calcination is carried out at a temperature generally from 350 to 750° C., preferably a temperature in the range of from 450 to 650° C. The effect of the calcination treatment is to remove (crystal) water, to decompose volatile decomposition products and to convert organic and inorganic compounds to their respective oxides.
However, calcination naturally involves some cost both in terms of the process and equipment. Moreover, there is possibly uncontrolled cracking and tension in the shaped catalyst or catalyst precursor which is undesired. There is also the problem of formation of unwanted compounds such as cobalt titanate. All these factors limit the range and types of compounds that can be used in catalyst formation, as well as reducing the activity of the catalyst formed.
WO 2005/030680 indicates that the calcination step is optional in the preparation of a titania comprising catalyst or catalyst precursor wherein at least 50 wt % of the crystalline titania is present as brookite. This document does not elaborate on a process for preparing such a catalyst or catalyst precursor in which the calcination step is omitted.
It is one object of the present invention to improve the process for preparing a catalyst or catalyst precursor.